susan

SUSAN corner detector. More...

Functions
AFAPI features	susan (const array &in, const unsigned radius=3, const float diff_thr=32.0f, const float geom_thr=10.0f, const float feature_ratio=0.05f, const unsigned edge=3)
	C++ Interface for SUSAN corner detector. More...
AFAPI af_err	af_susan (af_features *out, const af_array in, const unsigned radius, const float diff_thr, const float geom_thr, const float feature_ratio, const unsigned edge)
	C Interface for SUSAN corner detector. More...

Detailed Description

SUSAN corner detector.

SUSAN is an acronym standing for Smallest Univalue Segment Assimilating Nucleus. This method places a circular disc over the pixel to be tested (a.k.a nucleus) to compute the corner measure of that corresponding pixel. The region covered by the circular disc is M, and a pixel in this region is represented by \(\vec{m} \in M\) where \(\vec{m}_0\) is the nucleus. Every pixel in the region is compared to the nucleus using the following comparison function:

\( c(\vec{m}) = e^{-{(({I(\vec{m}) - I(\vec{m}_0))} / t})^6}\)

where t is radius of the region, I is the brightness of the pixel.

Response of SUSAN operator is given by the following equation:

\( R(M) = \begin{cases} g - n(M) \quad \text{if } n(M) < g\\ 0 \quad \text{otherwise},\\ \end{cases}\)

where \( n(M) = \sum\nolimits_{\vec{m} \in M} c(\vec{m})\), g is named the geometric threshold and n is the number of pixels in the mask which are within t of the nucleus.

Importance of the parameters, t and g is explained below:

• t determines how similar points have to be to the nucleusbefore they are considered to be a part of the univalue segment
• g determines the minimum size of the univalue segment. For a large enough g, SUSAN operator becomes an edge dectector.

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Function Documentation

af_susan()

AFAPI af_err af_susan	(	af_features *	out,
		const af_array	in,
		const unsigned	radius,
		const float	diff_thr,
		const float	geom_thr,
		const float	feature_ratio,
		const unsigned	edge
	)

C Interface for SUSAN corner detector.

Parameters

[out]	out	is af_features struct composed of arrays for x and y coordinates, score, orientation and size of selected features
[in]	in	is input grayscale/intensity image
[in]	radius	nucleus radius for each pixel neighborhood
[in]	diff_thr	intensity difference threshold a.k.a t from equations in description
[in]	geom_thr	geometric threshold
[in]	feature_ratio	is maximum number of features that will be returned by the function
[in]	edge	indicates how many pixels width area should be skipped for corner detection

Returns

AF_SUCCESS if SUSAN corner detection is successfull, otherwise an appropriate error code is returned.

Note

If in is a 3d array, a batch operation will be performed.

susan()

AFAPI features susan	(	const array &	in,
		const unsigned	radius = 3,
		const float	diff_thr = 32.0f,
		const float	geom_thr = 10.0f,
		const float	feature_ratio = 0.05f,
		const unsigned	edge = 3
	)

C++ Interface for SUSAN corner detector.

Parameters

[in]	in	is input grayscale/intensity image
[in]	radius	nucleus radius for each pixel neighborhood
[in]	diff_thr	intensity difference threshold
[in]	geom_thr	geometric threshold a.k.a t from equations in description
[in]	feature_ratio	is maximum number of features that will be returned by the function
[in]	edge	indicates how many pixels width area should be skipped for corner detection

Returns

If SUSAN corner detection is successfull returns an object of Features class, composed of arrays for x and y coordinates, score, orientation and size of selected features, otherwise exception is thrown.

Note

If in is a 3d array, a batch operation will be performed.